# Definition:Rank (Linear Algebra)

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## Definition

### Linear Transformation

Let $\phi$ be a linear transformation from one vector space to another.

Let the image of $\phi$ be finite-dimensional.

Then its dimension is called the **rank of $\phi$** and is denoted $\rho \left({\phi}\right)$.

### Matrix

Let $K$ be a field.

Let $\mathbf A$ be an $m \times n$ matrix over $K$.

Then the **rank** of $\mathbf A$, denoted $\rho \left({\mathbf A}\right)$, is the dimension of the subspace of $K^m$ generated by the columns of $\mathbf A$.

That is, it is the dimension of the column space of $\mathbf A$.